Utilization of solar energy can be classified as solar-photovoltaic and solar-thermal. Solar photovoltaic (PV) converts photon energy directly into electricity. The other is solar-thermal, which typically converts photon energy into heat stored in a terrestrial heat source such as a fluid, usually through an optical concentrator, and uses mechanical heat engines to generate electricity. Photovoltaic cells can be used on rooftops, while the solar-thermal energy conversion by mechanical heat engines is more suitable for large-scale power generation applications.
While the current solar-thermal to electricity conversion relies on steam-generation and mechanical heat engines, the prospect of using thermoelectric generator materials to convert solar energy first into heat and then into electricity has been pursued, but has not been widely utilized because of the low efficiency of thermoelectric devices. Thermoelectric power generation relies on the Seebeck effect in solid materials to convert thermal energy into electricity. The theoretical energy conversion efficiency ηte of a thermoelectric device operating between a hot-side temperature Th and a cold-side temperature Tc is given by
      η    te    =            (              1        -                              T            c                                T            h                              )        ⁢                                        1            +            ZT                          -        1                                          1            +            ZT                          +                              T            c                    /                      T            h                              where the factor (1−Tc/Th) is the Carnot efficiency, and the second factor is determined by the thermoelectric figure of merit Z and the average temperature T [=0.5(Th+Tc)] of the thermoelectric materials. The thermoelectric figure of merit (Z) is related to the material's Seebeck coefficient S, electrical conductivity σ, and thermal conductivity k via Z=S2σ/k. Calculations based on this efficiency suggest that with a ZT between 1-2, a thermoelectric device working between 303-500 K can have an efficiency of 9-14%, while the efficiency of a thermoelectric device operating between 300-1000 K with a ZT between 1-2 can reach 17-25%.
However, achieving such working conditions in a solar-thermoelectric generator has proven elusive. Indeed, heat losses and the ability to provide adequate thermal concentration for such devices remain problematic. Accordingly, a need exists for providing improved techniques related to solar thermoelectric generation.